PROCESS FOR PREPARING A POLYBENZOXAZINE-DERIVED CARBON MEMBRANE, CARBON MEMBRANE, USE OF SAID MEMBRANE FOR SEPARATING INDUSTRIAL GASES AND PERMEATION MODULE

Abstract

The present disclosure describes a process of obtaining a carbon membrane derived from polymer polybenzoxazine, for improved separation of gases with different kinetic diameters such as helium (2.60 ), hydrogen (2.89 ), carbon dioxide (3,30 ), oxygen (3.46 ), nitrogen (3.64 ), carbon monoxide (3.70 ), methane (3.80 ), ethylene (4.23 ) and ethane (4.42 ) from the molecular sieving mechanism.

Claims

1. A process for preparing polybenzoxazine (PBZ)-derived carbon membranes, the process comprising: i. preparing a precursor polymer solution; ii. coating a porous support with the precursor polymer solution or spreading the precursor polymer solution on a substrate to prepare one or more supporting or self-supporting membranes; iii. crosslinking a polymeric chain based on a benzoxazine monomer curing protocol; iv. controlling a thermal decomposition protocol of one or more crosslinked membranes; and v. storing the one or more crosslinked membranes.

2. The process of claim 1, wherein step (i) the polymer solution includes polybenzoxazine (PBZ), and wherein the polybenzoxazine (PBZ) comprises a synthetic or a derivation from renewable sources.

3. The process of claim 1, wherein step (i) the polymeric solution is prepared, with or without heating, by dissolving BZ in an organic solvent or from the synthesis of PBZ using a phenol, an amine, and an aldehyde.

4. The process of claim 3, wherein the organic solvent comprises methyl ethyl ketone, chloroform, n-methyl-2-pyrrolidone, hexane, dimethylacetamide, dimethylformamide, or toluene, or mixtures thereof to solubilize the polymer.

5. The process of claim 3, wherein a compound from a renewable source comprises (a) one or more of lignin, resveratrol, eugenol, guaiacol, catechol or vanillin is used as phenol, or (b) synthetic phenolic compounds comprising one or more of bisphenol A, bisphenol f, resorcinol, trihydric phenol, or 2-aminophenol.

6. The process of claim 3, wherein one or more of aniline, furfurylamine, ethylenediamine, curarin, octafecilamine, triethylamine, or methylenedianiline is used, and wherein one or more of benzaldehyde, valeraldehyde, or dimethylformaldehyde is used as aldehyde.

7. The process of claim 2, wherein step (i) a curing agent is added in concentrations between 5 and 30% (w/w) to increase crosslinking density of a PBZ polymer chain.

8. The process of claim 2, wherein step (i) an organic solvent is added to control viscosity of the benzoxazine polymeric solution.

9. The process of claim 1, wherein step (i) the concentration of the polymeric solution relates to thickness of a desired selective layer between 5 and 80% (w/w) polymer.

10. The process of claim 1, wherein step (i) after preparation, the polymeric solution is subjected to an ultrasonic bath or vacuum, with or without heating to eliminate bubbles.

11. The process of claim 1, wherein the polymeric solution obtained in step (i), with or without curing agent, is used in manufacture of the supported or self-supported membranes, and wherein the membranes comprise a flat, tubular, or hollow fiber configuration.

12. The process of claim 1, wherein step (ii) the polymeric solution is used to cover a non-selective porous support, wherein the support has a flat or tubular shape and is manufactured in one or more of alumina, silicon carbide, metallic material, with or without adding additives, or non-woven fabrics.

13. The process of claim 1, wherein step (ii) the polymeric solution is used to deposit the polymeric solution on tubular supports, and wherein deposition is carried out on an inner or an outer surface of the tubular supports.

14. The process of claim 1, wherein step (ii) includes coating on flat or tubular supports and is carried out by dip coating or spin coating.

15. The process of claim 14, wherein in dip coating, the ends of porous ceramic tubes are capped, wherein the tubes are slowly dipped into the polymeric solution for a predetermined time of between 30 and 600 seconds, wherein subsequently, the tubular ceramic supports are slowly removed from the precursor polymeric solution, wherein the tubes covered with the polymeric layer is subjected to a new coating cycle, which varies between 0 and 5 additional cycles, wherein coating is carried out at room temperature or at a controlled temperature, and wherein the membranes are dried at room temperature or at a controlled temperature until the solvent evaporates.

16. The process of claim 14, wherein in spin coating, the polymeric solution is deposited onto the surface of a support attached to a rod or base with a constant rotational angular speed ranging from 100 to 2000 rpm, wherein coating is carried out at room temperature or inside a temperature-controlled oven, and wherein the membranes are dried at room temperature or in a temperature-controlled oven until the solvent evaporates.

17. The process of claim 1, wherein step (iii) the membranes are formed through the crosslinking, wherein benzoxazine polymerizes by opening of the oxazine ring, and wherein the crosslinking process is thermal, chemical or by ultraviolet radiation, with or without additional catalysts or additives.

18. The process of claim 17, wherein additional catalysts or additives are selected from the group consisting of: polyaniline, 2,4-Di-tert-butylphenol, metal diethyl dithiocarbamates, tetramethylthiuram disulfide, zinc stearate, sulfur, thiols, ammonium salt, metal complexes of acetylacetonates, cyanuric chloride, Lewis acids, imidazoles, alkylenic acids, cyanate esters, p-toluenesulfonic acid, 2-ethyl-4-methylimidazole, adipic acid, and strong bases.

19. The process of claim 17, wherein in the thermal crosslinking, the polymeric membrane is subjected to heat treatment in a convection/air circulation or drying oven, in a temperature range of 80 and 350 C., for a pre-established time of between 3 and 12 hours by using a stepwise increase in temperature at intervals ranging from 10 to 50 C., with isothermal levels of 15 to 120 min.

20. The process of claim 1, wherein step (iii) the curing protocol promotes thermal adjustment of the final properties of the PBZ polymeric membranes, and wherein the benzoxazine monomers exhibit thermoplastic behavior and become thermoset.

21. The process of claim 20, wherein for the curing protocol, the cationic reaction of oxazine ring opening takes place, thereby to cause chain polymerization and formation of crosslinked structures.

22. The process of claim 21, wherein the greater the degree of curing, the greater the percentage of polybenzoxazine structures distinguished by the open ring structure.

23. The process of claim 22, wherein the pressure of the curing process is between 1 and 100 atm under atmospheric pressure.

24. The process of claim 1, wherein step (iv) from the pyrolysis protocol of the self-supported or supported polymeric membrane, a thin and homogeneous PBZ carbon selective membrane is formed.

25. The process of claim 24, wherein the thermal decomposition protocol is carried out under vacuum or in an inert atmosphere comprising nitrogen, argon, helium, or mixtures thereof, or an oxidizing atmosphere is used in the first stages of pyrolysis up to a temperature of 400 C.

26. The process of claim 25, wherein before the start of pyrolysis, a purge is carried out with the atmosphere used in the process and the prepared membrane is inserted into a quartz reactor located inside a temperature-controlled oven.

27. The process of any one of claim 26, wherein the pyrolysis protocol is carried out in two stages, and wherein the first stage takes place on a heating ramp from 90 to 300 C., with a constant heating rate value between 1 and 10 C..Math.min.sup.1, upon reaching the final temperature of the first stage, this temperature condition is maintained for a fixed period of up to 120 min, and in the second stage the system continues to heat at a constant heating rate between 1 and 10 C..Math.min.sup.1, until the final pyrolysis temperature, which is between 30 and 1000 C.

28. The process of claim 27, wherein the first step is carried out in an oxidizing atmosphere.

29. The process of claim 27, wherein the final temperature can optionally be maintained for a fixed period of up to 120 min.

30. The process of claim 27, wherein a pore activation step in an oxidizing atmosphere between 60 and 1000 C. is carried out.

31. The process of claim 27, wherein at the end of the pyrolysis protocol the controlled cooling process is carried out at a cooling rate of up to 10 C..Math.min.sup.1, up to room temperature, under the atmosphere used in the pyrolysis process, and cooling is carried out naturally, without controlling the cooling rate.

32. The process of claim 1, wherein in step (v) the membranes are stored in a desiccator with silica and in an ambient, oxidizing, vacuum, inert, or wet or dry atmosphere.

33. A PBZ-derived carbon membrane comprising a supported or self-supported structure and a flat, tubular, or hollow fiber configuration.

34. The membrane of claim 33, further comprising a porosity having a bimodal pore size distribution composed of ultramicropores of <7 and micropores of 7 to 20 .

35. The membrane of claim 33, wherein the membrane has mechanical and thermal strength, thereby allowing use under different pressure conditions of up to 100 bar and temperatures of up to 500 C.

36. The membrane of claim 35, wherein the membrane has chemical stability in contact with solvents, acidic and basic media, and resistance to a wide pH range of from 0 to 14.

37. The membrane of claim 36, wherein the membrane has high selectivity for different gas pairs, and wherein the selectivity is above 20 for CO.sub.2/N.sub.2 and CO.sub.2/CH.sub.4 gas pairs.

38. A method of use of a PBZ-derived carbon membrane comprising gas separating from a feed stream composed diameters of different gas molecules having similar kinetic.

39. The method of claim 38, wherein the method takes place through a molecular sieving mechanism and separates industrial gases that have different or similar kinetic diameters.

40. The method of claim 38, wherein gas molecules comprise C.sub.2H.sub.4, C.sub.2H.sub.6, C.sub.3H.sub.6, C.sub.3H.sub.3, H.sub.2S, CO.sub.2, CH.sub.4, O.sub.2, N.sub.2, He, H.sub.2, or mixtures thereof.

41. The method of claim 38, wherein the membrane is used in: industrial gas separation systems including C.sub.2H.sub.4/C.sub.2H.sub.6, C.sub.3H.sub.6/C.sub.3H.sub.8, CO.sub.2/CH.sub.4, O.sub.2/N.sub.2, CO.sub.2/N.sub.2, H.sub.2/N.sub.2, H.sub.2S/CH.sub.4, not limited to these, or separation of olefins from a gas stream containing C.sub.2H.sub.6, C.sub.3H.sub.8, CO.sub.2, CO, CH.sub.4, or N.sub.2.

42. A permeation module comprising an enclosure capable of allowing operation of the membrane under temperature and pressure conditions as well as in a geometry configured for operation of the membrane.

43. The module of claim 42, wherein the module comprises a flat, tubular or hollow fiber configuration, and wherein the module is composed of three main parts: the central body of the module machined in 310 stainless steel, which contains the supported membrane and two parts at opposite ends, equipped with openings for coupling the feed, concentrate, drag gas and permeate streams.

44. The module of claim 42, wherein the module sealing and membrane fixation occur through the use of o-rings and gaskets, and inside the module, the feed stream is contacted with the PBZ carbon membrane self-supported or deposited on the support, the permeate stream results from gases that permeate the surface of the membrane.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0054] To provide a total and full visualization of the goal of the present disclosure, the figures are presented below, which are referred to herein, as follows.

[0055] FIG. 1 illustrates an SEM image of the PBZ-derived carbon membrane supported at 10,000 magnification according to embodiments of the disclosure.

[0056] FIG. 2 illustrates in () the flat supports uniformly covered with the PBZ polymeric solutionbefore the curing process; in (B) flat supports with non-adhered PBZ polymeric solution are illustrated; in (C) tubular supports efficiently covered with PBZafter a curing process at a final temperature of 200 C. and in (D) the intrusion (matte coating) of polymeric solution in the tubular support is representedafter a curing process at a final temperature of 200 C. according to embodiments of the disclosure.

[0057] FIG. 3 illustrates in () and (C) a selective homogeneous PBZ-derived carbon layer; in (B) and (D) a selective PBZ-derived carbon layer is illustrated with surface defects and detachment from the support according to embodiments of the disclosure.

[0058] FIG. 4 illustrates the FTIR spectrum of PBZ polymeric films cured at different final temperatures: 25 C. (PBZ-25), 150 C. (PBZ-150) and 200 C. (PBZ-200) according to embodiments of the disclosure.

[0059] FIG. 5 illustrates the TGA and DTG curves of PBZ polymeric films cured at different final temperatures: 25 C. (PBZ-25), 150 C. (PBZ-150) and 200 C. (PBZ-200) according to embodiments of the disclosure.

[0060] FIG. 6 illustrates in (A) the SEM-FEG image of the cross section of the MCPBZ-150 carbon membrane (cured at a final temperature of 150 C. and pyrolyzed at a final temperature of 600 C.) and in (B) the EDS mapping of the cross section of the supported carbon membrane according to embodiments of the disclosure.

[0061] FIG. 7 illustrates in (A) a transmission electron microscopy image of the MCPBZ-200 carbon film (cured at a final temperature of 200 C. and pyrolyzed at a final temperature of 600 C.); in (B) the electron diffraction of the amorphous region and in (C) the electron diffraction of the crystalline region according to embodiments of the disclosure.

[0062] FIG. 8 illustrates in (A) the pore distribution and in (B) the accumulated pore volume for MCPBZ-150 and MCPBZ-200 according to embodiments of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0063] The present disclosure relates, in a first embodiment, to a process for developing carbon membranes derived from PBZ. Said process comprises the following steps: [0064] i. preparing the precursor polymer solution; [0065] ii. coating a porous support with the precursor polymer solution or spreading the precursor polymer solution on a substrate for preparing self-supporting membranes; [0066] iii. crosslinking process (benzoxazine monomer curing protocol); [0067] iv. controlled thermal decomposition protocol (pyrolysis) of the crosslinked membrane; [0068] v. membrane storage.

[0069] The present disclosure further describes analysis of performance through permeation tests of pure gases and mixtures through carbon membranes derived from PBZ.

[0070] To demonstrate the potential of said process, the present disclosure will be described in more detail in terms of the steps performed and their respective parameters.

[0071] The benzoxazine precursor polymer can be any polybenzoxazine, whether synthetic or derived from renewable sources. The polymeric benzoxazine (BZ) solution can be prepared, with or without heating, from dissolving the commercial prepolymer benzoxazine precursor in an organic solvent or from the synthesis of PBZ using a phenol, an amine, and an aldehyde. The organic solvent can be methyl ethyl ketone, chloroform, n-methyl-2-pyrrolidone, hexane, dimethylacetamide, dimethylformamide, toluene, not limited to these, or mixtures thereof, ensuring solubilization of the polymer.

[0072] Furthermore, in the synthesis of PBZ, a compound from a renewable source such as lignin, cardanol, resveratrol, eugenol, guaiacol, catechol and vanillin, not limited to these, or synthetic phenolic compounds such as bisphenol A, bisphenol f, resorcinol, can be used as phenol. trihydric phenol, 2-aminophenol, among other phenolic compounds, but not limited to these, can be used as phenol. Furthermore, aniline, furfurylamine, ethylenediamine, curain, octafecylamine, triethylamine, methylenedianiline, among others, can be used as amines; and formaldehyde, para-formaldehyde, benzaldehyde, valeraldehyde, dimethylformaldehyde, not limited to these, can be used as aldehyde.

[0073] During the preparation of the polymeric solution, a curing agent can be added in order to increase the crosslinking density (degree of cure) of the PBZ polymer chain. The curing agent can be added at concentrations between 5 and 30% (w/w). To control viscosity of the benzoxazine polymer solution an organic solvent can be added. Concentration of the polymer solution is related to the thickness of the desired selective layer, so it can be used between 5 and 80% (w/w) of polymer. After preparing the polymeric solution, it can be subjected to an ultrasonic or vacuum bath, with or without heating, in order to eliminate bubbles formed in the previous steps.

[0074] The prepared polymeric solution, with or without curing agent, is used in the manufacture of self-supporting membranes prepared in flat configuration using a casting or electrospinning technique, and in the extrusion hollow fiber configuration, not limited to these manufacturing processes. Furthermore, the BZ polymeric solution can be used to coat a non-selective porous support. The support can be flat or tubular in shape and can be made of alumina, silicon carbide, metallic material, with or without the addition of additives, and non-woven fabrics. In the deposition of the polymeric solution on tubular supports, coating can be carried out on the internal or external surface of the tube.

[0075] The coating methodology on supports (flat or tubular) can be carried out by immersion (dip coating) or by rotation (spin coating).

[0076] Coatings with PBZ polymeric solutions can be carried out on the outside of ceramic tubes using the dip coating method. The ends of porous ceramic tubes are capped, and the tubes are slowly dipped into the polymeric solution for a predetermined time of between 30 and 600 seconds. Subsequently, the ceramic support is slowly removed from the solution so as to allow the excess to flow due to the action of gravitational force. The tubes covered with the polymeric layer can be subjected to new cycles, ranging between 0 and 5 additional cycles, following the same methodology. This process can be carried out at room temperature or at a controlled temperature. The membranes are dried at room temperature or in a temperature-controlled oven so that the solvent evaporates.

[0077] In the spin coating methodology, the polymeric solution is deposited on the surface of a support attached to a rod or base at a constant angular spinning speed that can range from 100 to 2000 rpm. The coating process can be carried out at room temperature or in a temperature-controlled oven. The membranes are a room temperature or in a temperature-controlled oven so that the solvent evaporates.

[0078] After the supported or self-supported membrane manufacturing process, BZ polymeric membranes are formed through the process of crosslinking the benzoxazine pre-polymer, in which BZ rapidly polymerize through oxazine ring-opening polymerization. The crosslinking process can be thermal, chemical or by ultraviolet radiation, with or without additional catalysts or additives, such as polyaniline, 2,4-Di-tert-butylphenol, metal diethyl dithiocarbamates, tetramethylthiuram disulfide, zinc stearate, sulfur, thiols, ammonium salt, metal complexes of acetylacetonates, cyanuric chloride, Lewis acids, imidazoles, alkylenic acids, cyanate esters, p-toluenesulfonic acid, 2-ethyl-4-methylimidazole, adipic acid, strong bases such as sodium hydroxide or potassium hydroxide, among other catalysts and additives, but not limited to them. BZ prepolymers (monomers) exhibit thermoplastic behavior, becoming thermorigid after the curing process, so the curing process promotes the thermal adjustment of the final properties of PBZ polymeric membranes.

[0079] Prior to the curing process, the benzoxazine membrane has a benzene ring linked to an oxazine ring, characterized by a six-membered heterocyclic composed of oxygen and nitrogen atoms, according to the structure:

##STR00001##

[0080] During the BZ curing process, the cationic reaction of oxazine ring opening takes place, causing chain polymerization and forming crosslinked structures such as the following:

##STR00002##

[0081] The number of crosslinked structures is generally related to the curing protocol. Depending on the temperatures and isotherms employed in the curing process, different amounts of closed oxazine ring and open benzoxazine ring structures are formed. The greater the degree of curing, the greater the percentage of polybenzoxazine structures characterized by the open ring structure.

[0082] By changing the curing protocol variables, such as time at temperature levels, final temperature, and heating rate, it is possible to obtain polymeric membranes with different degrees of crosslinking and, consequently, different structures. In the thermal crosslinking process (thermal curing process), the BZ polymeric membrane is subjected to a well-defined thermal treatment, which can be carried out in a convection/air circulation or drying oven, in the range of from 80 and 350 C., for a pre-established time of from 3 to 12 hours, using a gradual increase in temperature at intervals ranging from 10 to 50 C., with isothermal plateaus of 15 to 120 min. With regard to the pressure of the curing process, the polymeric membrane can be crosslinked between 1 and 100 atm, preferably under atmospheric pressure.

[0083] Formation of a thin and homogeneous carbon-selective layer of PBZ occurs from pyrolysis (thermal degradation) of the self-supported or supported polymeric membrane. The pyrolysis process can be carried out under vacuum or in an inert atmosphere (nitrogen, argon, helium, or mixtures thereof), it is also possible to use an oxidizing atmosphere in the first stages of pyrolysis up to 400 C. The prepared membrane is inserted inside a quartz reactor located inside a temperature-controlled oven. Before starting pyrolysis, a purge is carried out with the atmosphere used in the process.

[0084] The pyrolysis protocol can be carried out in two stages, the first one taking place on a heating ramp from 90 to 300 C., with a constant heating rate value between 1 and 10 C./min, upon reaching the final temperature of the first stage, this temperature condition can be maintained for a fixed period of up to 120 min. This step can also be carried out in an oxidizing atmosphere. In the second step, the system continues to heat at a constant heating rate between 1 and 10 C./min, until the final pyrolysis temperature, which can be between 30 and 1000 C. is reached. The final temperature can be maintained for a fixed period of up to 120 min. Furthermore, it is possible to carry out a pore activation step in an oxidizing atmosphere between 60 and 1000 C. At the end of the pyrolysis protocol, the controlled cooling process can be carried out, at a cooling rate of up to 10 C./min, to room temperature, under the atmosphere used in the pyrolysis process. Cooling can also be carried out naturally, without controlling the cooling rate.

[0085] After the pyrolysis and cooling process, the PBZ carbon membranes can be stored, until use, in a desiccator with silica and in an ambient, oxidizing, vacuum or inert atmosphere. Furthermore, storage can be carried out in a humid or dry atmosphere.

[0086] Thus, the present disclosure describes, in a second embodiment, carbon membranes derived from PBZ obtained by said process. The main features of carbon membranes consist of: [0087] a. porosity, bimodal pore size distribution composed of ultramicropores (<7 ) and micropores (7 to 20 ); [0088] b. mechanical and thermal strength, allowing the membranes to be used under different pressure (up to 100 bar) and temperature (up to 500 C.) conditions; [0089] c. chemical stability, resistance to a wide pH range (0 to 14) and in contact with solvents, acidic and basic media; [0090] d. high selectivities for different gas pairs. Selectivities for CO.sub.2/N.sub.2 and CO.sub.2/CH.sub.4 gas pairs greater then 20, values higher than those described for commercial polymeric membranes.

[0091] The membranes are supported or self-supported and can have a flat, tubular, or hollow fiber configuration. The main benefits of the membranes are: [0092] a. high selectivity to certain gas pairs, which provides an efficient separation of industrial gases, obtaining purified streams of the gases of interest; [0093] b. greater control of gas permeability from the curing protocol; [0094] c. thermal and chemical stability suitable for real industrial processes that operate under mild temperature and pressure conditions; [0095] d. possibility of controlling the structure of the carbon membrane by adjusting parameters of its manufacturing process; [0096] e. increased selectivity and permeability of the gases of interest due to the interaction of gas molecules with the functional groups remaining in the carbon membrane chemical structure; [0097] f. greater applicability of the carbon membrane in gas separation systems.

[0098] In a third embodiment, the present disclosure discloses the use of said membrane in a gas separation process from a feed stream composed of different gas molecules, with similar kinetic diameters. The main action is through the molecular sieving mechanism and can purify/separate industrial gases that have different and/or similar kinetic diameters.

[0099] The mixed matrix carbon membrane can be used in industrial gas separation systems including C.sub.2H.sub.4/C.sub.2H.sub.6, C.sub.3H.sub.6/C.sub.3H.sub.3, CO.sub.2/CH.sub.4, O.sub.2/N.sub.2 to separate olefins from a gas stream containing C.sub.2H.sub.6, C.sub.3H.sub.8, CO.sub.2, CO, CH.sub.4, N.sub.2, for example.

[0100] In a fourth embodiment, the present disclosure defines a module for said membrane. The module comprises an enclosure capable of withstanding the temperature and pressure of use in the gas separation process.

[0101] In this sense, a permeation system can be composed of flat, tubular, or hollow fiber modules, depending on the configuration of the membrane used. Inside the module, the feed stream is contacted with the self-supporting PBZ carbon layer or deposited on the support. The permeate stream results from gases that permeate the surface of the membrane. The module is composed of three main parts: the central body of the module, which contains the supported membrane and two pieces at opposite ends, equipped with openings for coupling the feed stream, concentrate stream, gas drag stream and permeate stream. The module body is machined from 310 stainless steel or similar material, capable of withstanding the temperature and pressure conditions required by the permeation process. Sealing the module and fixing the membrane is done by using o-rings and gaskets, which guarantee the tightness of the gases used.

[0102] The main features of these modules can be described as: [0103] Regarding the presence of two inlet streams and two outlet streams: the feed stream, which contains the gases to be separated, the permeate stream, which contains the mixture of gases that permeate the membrane, the concentrate stream, which contains the gases retained by the membrane and a drag stream, which aims to carry the permeate gases to a later stage of the process. [0104] Regarding the tightness of the module, it must promote the containment of gases used, as well as avoid the mixing of the feed and permeate streams. [0105] As for the geometry of the module, it is suitable for the configuration of the membrane being used, as defined in the first aspect, being tubular, flat, or hollow fiber.

[0106] To demonstrate the potential of the present disclosure, the embodiments listed above will be described in more detail through embodiment examples and practical examples, as well as the results obtained. It should be noted that the following description is only intended to clarify the understanding of the proposed disclosure and disclose in even more detail the embodiment of the disclosure without limiting it. Therefore, variables similar to the examples are also included in the scope of the disclosure.

EXAMPLES OF EMBODIMENTS

[0107] In one process embodiment, the BZ solution is prepared by dissolving commercial benzoxazine (20 to 80%, w/w) in methyl ethyl ketone (20 to 80% w/w) and adding a commercial curing agent (15 to 25% w/w), under magnetic stirring (100 to 400 rpm) and heating (50 to 100 C.). The polymer solution is degassed in a vacuum oven (100 to 150 C.) for 10 to 45 min. Then, the solution is deposited on a flat support using spin coating at a speed of 100 to 2000 rpm. The support with the polymer solution layer is subjected to solvent evaporation in an oven (30 to 90 C., for 8 to 24 h) and subsequently crosslinked in an oven, under atmospheric pressure, following the heating protocol: 80 C. (20 to 60 min), 100 C. (20 to 60 min), 120 C. (45 to 90 min), 150 C. (45 to 90 min), 180 C. (45 to 90 min), 200 C. (45 to 120 min), 220 C. (45 to 120 min) and 250 C. (45 to 120 min).

[0108] In one embodiment of the process, polybenzoxazine is synthesized from the reaction between a phenol (such as resorcinol or cardanol) and an amine (aniline or furfurylamine), in the presence of para-formaldehyde, under mechanical stirring and heating (80 to 150 C.). The formed benzoxazine monomer can have its viscosity adjusted using a solvent (chloroform or methyl ethyl ketone) and then the solution is spread on a hydrophobic glass plate, or Teflon plate or silicone substrate, with the aid of a spreading knife. The benzoxazine curing process takes place by heating in a convection oven following a heating protocol for 6 hours, with a temperature ramp from 140 C. to 200 C.

[0109] In one embodiment of the process, the supported polymeric membrane and the self-supported polymeric membrane are subjected to the pyrolysis process in order to manufacture the PBZ-derived carbon membrane. The manufactured polymeric membranes are inserted inside a quartz reactor located inside a temperature-controlled tubular furnace. Before starting pyrolysis, a purge is carried out with an inert atmosphere, although any inert gas can be used as a purge gas, as an example, nitrogen can be used at a flow rate of 2 to 3 L.Math.min.Math..sup.1. The pyrolysis protocol is carried out in two stages, the first stage taking place with a heating ramp from 90 to 300 C. at a constant heating rate value of 3 C..Math.min.sup.1. Upon reaching the final temperature of 300 C., this temperature condition is held for a fixed period of 120 min. In the second stage, the system continues to heat at a constant heating rate of 3 C. min.sup.1, until the final pyrolysis temperature of 600 C. The final temperature is maintained for a fixed period of 30 min. At the end of the steps, the controlled cooling process can be carried out at a cooling rate of 5 C. min.sup.1, to room temperature, under a nitrogen atmosphere.

[0110] In one embodiment of the process, the PBZ carbon membranes are stored in a desiccator containing silica and nitrogen atmosphere until use in the gas permeation system.

[0111] In one embodiment of the process, the gas permeation system is composed of a module machined from 310 stainless steel, with flat geometry. The module consists of an upper part, equipped with a side inlet for supplying gases (pure or mixtures) and a side outlet for purging the concentrate stream; a lower part equipped with a side inlet for the drag gas and a side outlet for purging the permeate stream. The upper and lower parts have circular cutouts in which o-rings of suitable diameter are placed, which allow the central part to fit; a central part of tubular shape to which the flat geometry membrane is attached. The module is closed using four screws, which press the o-rings against the bottom of the side parts and against the edge of the central cylinder, causing sealing of the module and the separation of the process streams.

[0112] In one embodiment of the process, gas mixtures or pure gases are fed into the module and the gas or gas mixture permeated through the membrane accumulates in a closed chamber. The increased pressure in the permeate chamber is monitored by a pressure transducer.

[0113] In one embodiment of the process, the concentrate and permeate stream is injected into a gas chromatograph to analyze its composition.

Practical Examples

Preparation of the Precursor Polymer Solution

[0114] PBZ polymeric membranes were prepared by dissolving the commercial benzoxazine (BZ) monomer (Araldite LZ 8291Huntsman) in methyl ethyl ketone (MEK), at a PBZ/MEK ratio of 40:60, in the presence of the curing agent (HZ 8293, Huntsman). BZ was added to a beaker and maintained under magnetic stirring at 230 rpm at 90 C. for 10 minutes, until the solution was homogenized, and viscosity was reduced. The MEK solvent was added to the solution, under magnetic stirring and heating, for 10 minutes. Afterwards, the curing agent was added (19%, v/v) to the system under stirring at 90 C. for 10 min. After complete solubilization, the solutions were used to prepare flat and supported polymeric membranes.

Preparation of Self-Supporting Polymer Film

[0115] The BZ/MEK polymeric solution (10 mL) was spread onto a silicone substrate using a glass rod. The films were dipped in a non-solvent bath composed of distilled water for 72 h. Subsequently, they were subjected to the thermal curing protocol. Self-supported benzoxazine polymeric films were prepared using the casting technique using the polymeric solutions previously described in order to characterize the polymeric material.

Coating of Porous Support with Precursor Polymeric Solution

[0116] The supported PBZ membranes were prepared from the deposition of the BZ/MEK polymeric solution on the surface of the flat ceramic support using spin coating. The ceramic support was attached to the equipment and spinned at 1000 rpm. The BZ polymeric solution (1.5 mL) was deposited on the support at a constant speed of 1,000 rpm for 30 seconds, characterizing a coating cycle. Six coating cycles were performed with a 30-second interval between them. Subsequently, the supported polymeric membranes were subjected to heating in an oven at 25 C. for 24 hours to evaporate the solvent and subsequent curing protocol. In order to compare the influence of the number of coatings on the carbon membrane performance, a carbon membrane was prepared with 5 coatings and cured at 150 C. (MCPBZ-150-5R).

Thermal Curing Protocol

[0117] The curing protocol is an essential step in developing a high-quality material with suitable properties for its application. In the present disclosure, five curing protocols were assessed for the development of PBZ-derived carbon membranes. PBZ polymeric membranes and self-supported films were subjected to the pyrolysis protocol in an oven with forced air convection, according to the protocols specified in Table 1.

TABLE-US-00001 TABLE 1 Curing protocol for PBZ polymeric membranes. Sample Curing protocol MCPBZ-25 25 C. for 3 h MCPBZ-150 80 C. for 1 h, 90 C. for 1 h, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, and 150 C. for 1 h. MCPBZ-200 80 C. for 1 h, 90 C. for 1 h, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 1 h, 180 C. for 1 h and 200 C. for 1 h. MCPBZ-220 80 C. for 1 h, 90 C. for 1 h, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 1 h, 180 C. for 1 h, 200 C. for 1 h and 220 C. for 1 h. MCPBZ-250 80 C. for 1 h, 90 C. for 1 h, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 1 h, 180 C. for 1 h, 200 C. for 1 h, 220 C. for 1 h and 250 C. for 1 h.

Preparation of PBZ-Derived Carbon Membranes

[0118] The supported polymeric PBZ films and membranes were subjected to the pyrolysis process to form carbon membranes. The membrane was inserted into a tubular furnace under a controlled atmosphere (inert, N.sub.2) at a rate of 2 mL.Math.min.sup.1, and the heating protocol at 90 C. was started and maintained for 30 min; the 3 C..Math.min.sup.1 rate was used until reaching a temperature of 300 C., which was maintained for 120 min and raised to 600 C. at the same heating rate and maintained at that temperature for 30 min. After heating, the system was cooled at a maximum cooling rate of 5 C..Math.min.sup.1 up to 100 C. The flow of N.sub.2 was kept constant throughout the pyrolysis process. After preparing the carbon membranes derived from PBZ, they were stored in a desiccator with silica.

Characterization of the Polymer Precursor and the Selective Carbon Layer Derived from PBZ

[0119] Chemical structures of the polymeric films were characterized by Fourier transform infrared spectroscopy (FTIR). Absorption spectra in the infrared region were obtained by the attenuated total reflection (ATR) module in a Perkin Elmer Frontier spectrometer in the wavenumber range between 4000 and 650 cm.sup.1, with 64 scans per spectrum and 4 cm.sup.1 resolution.

[0120] The polymeric films, precursors to CM, were characterized by thermogravimetric analysis (TGA) on a TA Instruments SDT Q600 equipment with to assess the degradation and thermal stability of the prepared films. Thermal properties of the materials were assessed in the temperature range between 3 and 700 C., in an inert nitrogen atmosphere (100 mL.Math.min.sup.1) with a heating rate of 10 C..Math.min.sup.1.

[0121] The cross-sectional morphology of the carbon membrane and adhesion of the carbon layer on the alumina support were investigated by field emission scanning electron microscopy (FEG-SEM). The samples were fractured with liquid nitrogen and the material fragments were deposited in stubs with a carbon ribbon and metallized with gold. Morphology of the samples was characterized using a scanning electron microscope model Inspect F50-FEI with a working voltage of 20 kV and point resolution of 1.2 nm. Furthermore, verification of polymer intrusion into the ceramic support was carried out based on the elemental analysis mapping of the cross section of the membrane supported on the energy dispersive X-ray analyzer coupled to the MEV-FEG.

[0122] Transmission electron microscopy (TEM) analysis was carried out on a Tecnai GM2100F microscope at 200 kV with electron diffraction, to evaluate the microstructure of the PBZ-derived carbon film. The polymeric film in powder form was dispersed in ethyl alcohol using an ultrasonic bath for 20 min. The dispersion was dripped onto the copper grid (300 mesh).

[0123] N.sub.2 adsorption and desorption analyzes were performed on a pore size analyzer (Nova 4200e, Quantachrome, France) to determine the average pore diameter, size distribution and pore volume of the PBZ-derived carbon films. The carbon samples were degassed at 300 C. for 6 h and the sorption and desorption process took place at 77 K.

Pure Gas Permeation Tests

[0124] Performance tests of flat carbon membranes prepared with 6 coating cycles, cured in different curing protocols and pyrolyzed at 600 C. (MCPBZ-25, MCPBZ-150, MCPBZ-200, MCPBZ-220 and MCPBZ-250) and the flat carbon membrane prepared with 5 coating cycles, cured at 150 C. and pyrolyzed at 600 C. (MCPBZ-150-6R) were carried out in a flat permeation cell. The system was subjected to vacuum for a period of 20 minutes between the permeation tests carried out with the different gases. To measure the gas flow in polymeric membranes, the constant volume method was used, with the pressure variation signal (dp/dt) being monitored using a pressure transducer connected to a data recording and collection system comprising a FieldLogger model recorder (NOVUS, Brazil) and a computer.

[0125] Permeability calculation (P) was carried out using Equation 1 below:

[00001]$\begin{array}{cc}P=\frac{V_{C}l{T}_{\mathrm{CNTP}}}{PA{T}_{\mathrm{amb}}{P}_{\mathrm{CNTP}}}\left(\frac{\mathrm{dp}}{\mathrm{dt}}\right)& \left(1\right)\end{array}$

where P is the permeability (cm.sup.3 cm cm.sup.2 s.sup.1 cmHg.sup.1 or Barrer, 1 Barrer=1.10.sup.10 cm.sup.3 cm cm.sup.2 s.sup.1 cmHg.sup.1), V.sub.c is the volume of the permeation cell downstream of the membrane (5.5 cm.sup.3), A and 1 are, respectively, the area (cm.sup.2) and thickness of the membrane (cm), P is the transmembrane pressure (cmHg), T.sub.Amb is the ambient temperature (K), T.sub.CNTP (273.15 K) is the temperature and P.sub.CNTP (76 cmHg) is the pressure at normal temperature and pressure conditions (CNTP) and dP/dt is the pressure increase rate in the permeate (cmHg s.sup.1). Tests were carried out at room temperature, in the range of from 15 to 30 C., and pressures set between 4 and 7 bar.

Permeation Tests of Gas Mixtures

[0126] In order to obtain information about the actual performance of the membrane produced by process, three gas mixtures were permeated, two of them being ternary mixtures composed of ethane, ethylene and CO.sub.2 and another binary mixture formed by CO.sub.2 and CH.sub.4, on an Agilent 8860 GC System gas chromatograph.

[0127] To start the gas permeation process, the membrane was inserted into the gas permeation module and vacuum was activated for 20 min to remove any gases present in the equipment. After vacuuming, the module was aligned to the chromatograph. Nitrogen was used as a drag gas in the process. Firstly, this gas was inserted into the permeate of the gas separation module, maintaining a constant flow at atmospheric pressure for 2 min, to clean the chromatograph loop and the connection line between the module and the chromatograph. Afterwards, the permeate outlet and gas injection valve were closed and the permeation process began. A constant pressure of 6 bar was maintained in the feed, with the previously prepared mixture. The permeation process took place until a gauge pressure of 0.2 bar was reached on the permeate side. Afterwards, nitrogen was inserted into the permeate chamber up to a gauge pressure of 1 bar, and then sent for analysis on the chromatograph.

[0128] The detector used was of the TCD type (Thermal Conductivity Detector) with two samples for each membrane. Data processing was carried out using the Data Analysis software from Agilent.

Results

Characterization of the Chemical Structure of the Cross-Linked Precursor Polymer at Different Curing Degrees

[0129] Characterization of the chemical structure and verification of the polymerization/crosslinking (curing process) of the PBZ polymeric membranes were carried out by FTIR. Polymerization of benzoxazine can occur from a heat treatment of the benzoxazine monomer, since the ring opening mechanism is a thermally activated chemical reaction. Chemical structure of the commercial benzoxazine monomer and crosslinked PBZ are presented below:

##STR00003##

[0130] In the present disclosure, crosslinking of the structure of the polymerized precursor polymer was verified in a well-defined curing protocol with a final temperature of 25, 150 and 200 C., samples PBZ-25, PBZ-150 and PBZ-200, respectively. The FTIR spectra of the polymeric films are shown in FIG. 4. The polymeric film cured at 25 C. showed characteristic absorption bands of the oxazine ring related to asymmetric and symmetric stretching of COC (aromatic), located at 1230 and 1030 cm.sup.1, respectively. Other bands related to the oxazine ring (tri-substituted aromatic ring) were observed in the range between 930 and 980 cm.sup.1. Furthermore, the absorption bands at 2930 and 1360 cm.sup.1 were related to vibrations of CH.sub.2 bonds of the aromatic rings and the stretching of the CN bond, respectively. Polymerization of benzoxazine using higher temperatures and longer curing protocol can be confirmed from the FTIR spectra. Intensity of the absorption bands located at 1230 and 1030 cm.sup.1 and in the range of from 930 to 950 cm.sup.1 were reduced, which can be attributed to the oxazine ring opening mechanism that promotes polymerization. Furthermore, there was an intensification of the absorption band at 1660 cm.sup.1 related to imine groups, formed by secondary reactions during the cure process. It was noted that the membranes polymerized using a cure protocol with a final temperature of 200 C. showed a higher degree of cure than the other membranes assessed, as their spectra showed greater reduction in the intensity of the absorption bands corresponding to the oxazine ring. The difference in the degree of cure of benzoxazine based on the change in the thermal cure protocol is not reported in the state-of-the-art documents.

Thermal Properties of the Crosslinked Precursor Polymer at Different Cure Degrees

[0131] thermal properties of PBZ polymer films cross-linked with different curing protocols (PBZ-25, PBZ-150 and PBZ-200) were evaluated by TGA in an inert nitrogen atmosphere, Table 2 and FIG. 5. From the TGA curves and its derivative (DTG), it was possible to verify that all films presented three main regions of mass loss. The initial mass loss, in the range of 20 to 150 C., is related to the evaporation of water molecules and free solvent. The second region of mass loss between 15 and 300 C. corresponds to the bound solvent, while the third region between 30 and 600 C. is attributed to degradation of the polymer backbone. The different curing processes affected the thermal properties of the precursor polymer, the higher the final curing temperature of the benzoxazine monomer, the greater the thermal stability of the polymer. Furthermore, it was observed that increasing the curing temperature caused a reduction in the percentage of mass loss related to free and bound solvent, in addition to slightly increasing the residue content at 700 C. These results may be related to the increased crosslinking density of the polymer chain with the increased final temperature of the thermal curing protocol. At this point, it should be highlighted that none of the prior art documents assess or indicate the relationship between the curing protocol and the thermal properties of the precursor polymer.

[0132] The residue content after pyrolysis is an important factor for the development of carbon membranes, as it affects the thickness of the selective carbon layer, which is directly related to the permeability of the membrane. The higher the residue content, the greater the final thickness of the carbon membrane.

TABLE-US-00002 TABLE 2 Results of thermogravimetric analysis of PBZ polymeric films. Mass Mass Mass loss from loss from T.sub.max of loss at 150 to 300 to main chain Residues 150 C. 300 C. 600 C. degradation at 700 C. Sample (%) (%) (%) ( C.) (%) MCPBZ-25 4.0 4.4 57.8 417.0 33.6 MCPBZ-150 0.9 4.0 55.7 414.0 34.8 MCPBZ-200 0.9 1.4 53.3 409.1 41.7

Structure and Adhesion of PBZ-Derived Carbon Membrane

[0133] The structure and adhesion of the PBZ-derived selective carbon layer on the flat support was evaluated by SEM-FEG, FIG. 6. The MCPBZ-150 carbon membrane presented a carbon layer apparently free of defects and cracks, with a thickness of about 8 m and effectively adhered to the flat support, without the presence of any interfacial voids between both materials. EDS spectroscopy was performed to verify the possible intrusion of the precursor polymer into the ceramic support, FIG. 6.B. The EDS mapping image of the MCPBZ-150 cross section showed a significant presence of carbon on the support surface (red color), indicating formation of the carbon layer. Furthermore, minor traces of carbon were identified inside the support, suggesting a low percentage of intrusion of the precursor polymer into the support. These results indicate the potential application of PBZ as a precursor polymer for carbon membranes, since they promoted the formation of a structure suitable for use as a membrane and characterized by a regular, selective surface fully adhered to the support. The prior art documents do not suggest the potential adhesion of the PBZ-based carbon material to a ceramic support, nor do they report the potential formation of a carbon structure free of cracks and defects on the support.

[0134] Based on transmission electron microscopy analysis combined with electron diffraction of MCPBZ-200, it was possible to verify the presence of disordered and crystalline structures. FIG. 7.A presents a stacked carbon film characterized by a disordered region (FIG. 7.B), responsible for the formation of ultramicropores in the membrane, in addition to a crystalline region (FIG. 7.C) characteristic of a graphitic structure with spacing between sheets of about 0.33 nm. These results indicate that the carbon membrane was effectively prepared, as the CM structure is characterized by regions containing amorphous carbon and small crystalline sites similar to graphene, which form a porous structure called turbostratic. CMs have a bimodal pore size distribution composed of ultramicropores (<7 ) and micropores (7 to 20 ). The prior art documents, which report the development of PBZ-derived carbon materials, did not perform TEM characterizations on the material. Furthermore, in these documents, there is no evidence of the formation of ultramicropores in PBZ-based carbon materials, an essential characteristic for gas transport to occur through the molecular sieving mechanism. The aforementioned documents only indicate the presence of micropores in carbon materials.

Characterization of Pores of PBZ-Derived Carbon Membranes

[0135] The distribution and volume of accumulated pores for MCPBZ-150 and MCPBZ-200 were verified from N.sub.2 sorption and desorption analysis, FIG. 8. According to FIG. 8.A, the MCPBZ-200 and MCPBZ-150 membranes presented predominant pores in the range of micro and ultramicropores, corroborating the electron diffraction results obtained by TEM, FIG. 7. It is observed that changing the curing protocol for the benzoxazine monomer to a higher final temperature caused the formation of pores having a radius of less than 5.5 , FIG. 8.A, combined with a smaller pore volume, FIG. 8.B. Furthermore, the average pore size of the membranes was also influenced by the curing protocol, the MCPBZ-200 membrane presented an average pore size of 4.597 , while for MCPBZ-150 the value found was 5.949 . These results may be related to a change in the free volume of the chemical structure of the precursor polymer, since the degree of polymer crosslinking is related to mobility of the polymer chain. The free volume of the precursor polymer chain directly affects the interplanar spacing between graphene layers of the carbon structures, the greater the free volume, the greater the interplanar spacing. It is worth noting that the state-of-the-art documents related to the development of carbonaceous materials derived from PBZ do not discuss the possibility of controlling pores by adjusting the curing protocol. The referenced documents report that pore adjustments can be carried out using the pyrolysis protocol, differing from the present disclosure.

Pure Gas Permeation Tests

[0136] The performance results of PBZ-derived carbon membranes supported in flat configuration are presented in Table 3. According to data analysis, the gas transport properties through CMs derived from PBZ are governed mainly by the molecular sieving mechanism, in which gases having distinct and very close kinetic diameters are separated with high efficiency. It was found that gaseous molecules with smaller kinetic diameter tended to pass through the carbon membrane structure more easily, since their size is smaller than the average pore size of the membrane. Larger gas molecules are retained by the structure, due to the larger kinetic diameter, according to the permeability results presented in Table 3. Furthermore, concomitantly with molecular sieving, the existence of interactions between the chemical structure of CM derived from PBZ (functional groups remaining after pyrolysis) and ethylene gas molecules was noted, promoting greater permeability to this gas compared to the permeability to nitrogen gas, which has a smaller kinetic diameter.

[0137] Performance tests of PBZ-derived MCs were carried out on samples prepared in different curing protocols. It was observed that the final curing temperature used in the polymerization of the precursor prepolymer directly affects the transport properties of the material. The higher the curing temperature employed during thermal crosslinking of the benzoxazine monomer, the lower the gas permeability through the membrane. This result may be related to the change in structure caused by the different final curing temperature, which influences the size and volume of pores and the free volume of the precursor polymer, corroborating the results of nitrogen sorption and desorption (FIG. 8). Furthermore, Table 4 shows that the performance tests for PBZ-derived CMs showed high values of ideal selectivity, potential for the separation of gases from emerging industrial processes, such as the separation of byproducts of the oxidative ethane dehydrogenation (ODH) (separation of CO.sub.2/C.sub.2H.sub.4, CO.sub.2/C.sub.2H.sub.6 e C.sub.2H.sub.4/C.sub.2H.sub.6 gas pairs), purification of natural gas (CO.sub.2/CH.sub.4), in obtaining nitrogen purified from air (N.sub.2/CO.sub.2) and the concentration of oxygen in the air (O.sub.2/N.sub.2). Furthermore, based on the selectivity results, it is observed that from a single precursor polymer it is possible to obtain carbon membranes for application in different industrial gas separation processes, since with the appropriate monomer curing protocol, it is possible to adjust the selectivity for the separation of industrial gas pairs of interest. Therefore, these results suggest the potential application of these materials in streams composed of different industrial gases.

TABLE-US-00003 TABLE 3 Results of pure gas permeability for carbon membranes prepared with 6 coating cycles, cured in different curing protocols and pyrolyzed at 600 C. Permeability (Barrer) He CO.sub.2 O.sub.2 N.sub.2 CH.sub.4 C.sub.2H.sub.4 C.sub.2H.sub.6 2.60 3.30 3.46 3.64 3.80 4.23 4.42 Membrane MCPBZ- NP 504 220 24 NP 15 2 25 MCPBZ- 1016 488 187 12 NP 19 0.8 150 MCPBZ- NP 350 154 19 3 10 0.4 200 MCPBZ- 618 390 163 13 NP 15 2.4 220 MCPBZ- 49 98 33 5 NP 9 0.8 250 NP = Permeation test not performed for this gas

TABLE-US-00004 TABLE 4 Optimal selectivity results for carbon membranes prepared with 6 coating cycles, cured in different curing protocols and pyrolyzed at 600 C. Optimal selectivity CO.sub.2/ CO.sub.2/ C.sub.2H.sub.4/ CO.sub.2/ CO.sub.2/ O.sub.2/ Membrane C.sub.2H.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.6 CH.sub.4 N.sub.2 N.sub.2 MCPBZ-25 34 252 8 NP 21 9 MCPBZ-150 26 610 32 NP 41 16 MCPBZ-200 35 875 25 117 19 8 MCPBZ-220 26 162 6 NP 30 13 MCPBZ-250 11 122 11 NP 20 7 NP = Permeation test not performed for this gas

[0138] The influence of the number of coating cycles of precursor polymeric solution on the support was also investigated. The carbon membrane prepared with 6 coating cycles, cured at 150 C. and pyrolyzed at 600 C. (MCPBZ-150) was compared with the carbon membrane prepared using 5 coating cycles, cured at 150 and pyrolyzed at 600 C. (MCPBZ-150-5R). Membranes with different numbers of coating cycles, Table 5 and Table 6, showed similar gas transport properties, with separation being characterized predominantly by the molecular sieving mechanism and with preferential interaction by ethylene gas. A greater permeation of pure gases is observed through the carbon membrane with fewer coatings (MCPBZ-150-5R), which may be related to the possible reduction in the thickness of the selective layer. Furthermore, the increased permeability of MCPBZ-150-5R as compared to MCPBZ-150 caused a reduction in the ideal selectivity of the gas pairs analyzed.

TABLE-US-00005 TABLE 5 Pure gas permeability results for carbon membranes prepared with different numbers of coating cycles. Permeability (Barrer) He CO.sub.2 O.sub.2 N.sub.2 CH.sub.4 C.sub.2H.sub.4 C.sub.2H.sub.6 2.6 3.30 3.46 3.64 3.80 4.23 4.42 Membrane MCPBZ-150 1016 488 187 12 NP 19 0.8 MCPBZ-150- 1276 609 228 16 NP 25 1.6 5R NP = Permeation test not performed for this gas

TABLE-US-00006 TABLE 6 Optimal selectivity results for carbon membranes prepared with different numbers of coating cycles. Optimal Selectivity CO.sub.2/ CO.sub.2/ C.sub.2H.sub.4/ CO.sub.2/ CO.sub.2/ O.sub.2/ Membrane C.sub.2H.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.6 CH.sub.4 N.sub.2 N.sub.2 MCPBZ-150 26 610 32 NP 41 16 MCPBZ-150-5R 24 380 16 NP 38 14 NP = Permeation test not performed for this gas

[0139] Permeations of C.sub.2H.sub.4 and C.sub.2H.sub.6 gases assessed in the present disclosure were not investigated in prior art documents that present the application of PBZ polymeric membranes and PBZ-derived carbon materials in gas separation. In studies on the preparation of polymeric membranes, the transport mechanism of H.sub.2, CO.sub.2, O.sub.2, CH.sub.4 and N.sub.2 gases was evaluated, which was classified as sorption-diffusion. The state of the art proposes the development of PBZ-modified SiO.sub.2 e ZrO.sub.2 ceramic-carbon membranes. The molecular sieving mechanism was identified only at the pyrolysis temperature of 750 C., related to the narrowing of the pores at this temperature. At the pyrolysis temperature of 550 C., the predominant mechanism was Knudsen diffusion. This difference in gas transportation was attributed to the higher pyrolysis temperature, which allows the complete pyrolytic transformation of, generating a narrowing of the pores and the formation of dense regions. Also, this result was found for a membrane composed of SiO.sub.2, ZrO.sub.2 and a small percentage of PBZ (0.25%, by mass, of the polymeric solution). Performance tests on gas separation were not carried out for the pure polymer. Therefore, it is not clear whether the molecular sieving is due to the inorganic material or the addition of PBZ. The state of the art, which classifies carbon materials derived from pure PBZ as molecular sieve, does not exemplify performance tests with different gases and does not provide any results demonstrating the presence of a structure containing regions of micro and ultramicropores. In all of the state of the art, there are no findings on the possibility of applying the developed materials for the separation of by-products originating from ethane ODH, olefins/paraffins and the concentration of oxygen in the air. Regarding the separation of olefins and paraffins, the prior art also does not report the interaction between the chemical structure of the PBZ-derived carbon membrane with the ethylene gas molecules, which facilitate permeation of this gas through the membrane.

Permeation Tests of Gas Mixtures

[0140] The separation properties of a membrane are best understood when using a synthetic mixture that closely matches the process conditions in which it will be applied. Therefore, permeation tests were carried out with three gas mixtures composed of: [0141] (i) 33% CO.sub.2, 31% C.sub.2H.sub.6 and 36% C.sub.2H.sub.4, [0142] (ii) 6.4% CO.sub.2, 82.7% C.sub.2H.sub.6 and 10.9% C.sub.2H.sub.4, [0143] (iii) 30% CO.sub.2 and 70% CH.sub.4. Mixtures composed of CO.sub.2, C.sub.2H.sub.4 and C.sub.2H.sub.6 represent the outlet streams of ethane ODH byproducts and the CO.sub.2 and CH.sub.4 mixture is related to purification of natural gas.

[0144] Ethane ODH consists of an exothermic process and takes place at temperatures below 550 C., characterizing itself as a highly energy-efficient process with environmental appeal, as it produces fewer amounts of NOx and CO.sub.2 gases, which are responsible for the greenhouse effect. However, four possible secondary reactions can occur during ODH of light paraffins, generating byproducts (carbon dioxide and carbon monoxide) that reduce ethane conversion and olefin yield. Therefore, to make ODH viable and competitive, it is necessary to increase selectivity of the separation process based on CO.sub.2 and CO separation from C.sub.2H.sub.4 and C.sub.2H.sub.6.

[0145] Permeation tests of gas mixtures were performed on a carbon membrane prepared with 6 coating cycles, cured at 150 C. and pyrolyzed at 600 C. The actual selectivities for the gas mixtures evaluated are presented in Table 7. These results indicate that the PBZ-derived carbon membrane has potential application for the separation of ethane ODH byproducts and for the purification of natural gas. It is important to highlight that the state of the art does not suggest that the prepared materials can be applied in this industrial process, nor does it present tests and indications for the application of PBZ-based materials in the separation of olefins and paraffins (C.sub.2H.sub.4/C.sub.2H.sub.6).

TABLE-US-00007 TABLE 7 Actual selectivity results for the different gas mixtures assessed. Mixture Actual selectivity composition (%) CO.sub.2/ CO.sub.2/ C.sub.2H.sub.4/ CO.sub.2/ Membrane CO.sub.2 C.sub.2H.sub.6 C.sub.2H.sub.4 CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.2H.sub.6 CH.sub.4 MCPBZ- 33 31 36 NP 50 11 4 NP 150-I MCPBZ- 6.4 82.7 10.9 NP 92 9 10 NP 150-II MCPBZ- 30 NP NP 70 NP NP NP 104 150-III NP = Permeation test not performed for this gas

Example 1

[0146] Polymeric solutions of commercial benzoxazine prepolymer (BZ), methyl ethyl ketone (MEK) and curing agent (HZ 8293, with confidential formulation) were prepared to be used as flat supported membranes. In a beaker, BZ (30 mL) was added and maintained under magnetic stirring at 230 rpm at 90 C. for 10 min, until the solution was homogenized and viscosity was reduced. MEK solvent (12 mL) was added to the solution under magnetic stirring and heating for 10 min. Then, the curing agent (5.7 mL) was added to the system under stirring at a temperature of 90 C. for 10 min. After complete solubilization, the solutions were used to prepare supported polymeric membranes. The supported membranes were prepared by deposition of the prepared polymeric solution on a flat alumina support using spin coating. The ceramic support was attached to the equipment and spinned at 1000 rpm. The BZ polymeric solution (1.5 mL) was deposited on the support at a constant speed of 1,000 rpm for 30 s, this procedure consisted of a coating cycle. This step was repeated 4 times, totaling 5 coating cycles. Subsequently, the supported polymeric membranes were subjected to heating in an oven at 25 C. for 24 h to evaporate the solvent.

[0147] The supported PBZ polymeric membranes were subjected to the thermal curing process according to the following heating protocol: 80 C. for 30 min, 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 60 min, 180 C. for 60 min and 200 C. for 90 min.

[0148] Formation of the PBZ-derived carbon molecular sieve membrane was carried out through the controlled thermal decomposition process, the so called pyrolysis process. The ceramic support coated with the PBZ polymeric solution crosslinked at 200 C. was inserted into a quartz reactor located inside a temperature-controlled tubular furnace. Prior to the start of pyrolysis, a purge was carried out with an inert nitrogen atmosphere at a flow rate of 2 L.Math.min.Math..sup.1. The pyrolysis protocol was carried out in two steps, the first one taking place on a heating ramp from 90 to 300 C. 1, with a constant heating rate value of 3 C..Math.min.sup.1, upon reaching the final temperature of 300 C., this temperature condition can be maintained for a fixed period of up to 120 min. In the second stage, the system continues to heat at a constant heating rate of 3 C..Math.min.sup.1, until the final pyrolysis temperature of 500 C. The final temperature was maintained for a fixed period of 30 min. At the end of the steps, the controlled cooling process was carried out at a maximum cooling rate of 5 C..Math.min.sup.1, up to a temperature of 30 C., under a nitrogen atmosphere.

[0149] The PBZ-derived carbon membranes were stored in a desiccator containing silica until use in the gas permeation system.

[0150] Gas permeation took place in a gas permeation system made of a module machined from 310 stainless steel, with flat geometry. The module consists of an upper part, equipped with a side inlet for supplying gases and a side outlet for purging the concentrate stream; a lower part equipped with a side inlet for the drag gas and a side outlet for purging the permeate stream. The upper and lower parts have circular cutouts in which o-rings of suitable diameter are placed, which allow the central part to fit; a central part of tubular shape to which the flat geometry membrane is attached. The module is carried using four screws, which press the o-rings against the bottom of the side parts and against the edge of the central cylinder, causing sealing of the module and the separation of the process streams. The gas permeated through the membrane accumulates in a closed chamber and the increase in pressure in this chamber is monitored by a pressure transducer. To assess the performance of the developed membranes, pure gases He, CO.sub.2, O.sub.2, N.sub.2, CH.sub.4, C.sub.2H.sub.4 and C.sub.2H.sub.6 and results of the permeation tests are presented in Table 8.

TABLE-US-00008 TABLE 8 Gas permeabilities and selectivities of gas pairs obtained for a PBZ-derived carbon membrane (MCPBZ-5R/200-500) manufactured from the deposition of 5 layers of polymeric solution on a flat ceramic support and with final curing and pyrolysis temperatures equal to 200 C. and 600 C., respectively. MCPBZ-5R/200-500 Pure Kinetic Permeance Optimal gas diameter (GPU) Gas pairs selectivity He 2.60 14 CO.sub.2/N.sub.2 18 CO.sub.2 3.30 16 CO.sub.2/CH.sub.4 40 O.sub.2 3.46 6 .sup.CO.sub.2/C.sub.2H.sub.4 27 N.sub.2 3.64 0.9 .sup.CO.sub.2/C.sub.2H.sub.6 160 CH.sub.4 3.80 0.4 O.sub.2/N.sub.2 7 C.sub.2H.sub.4 4.23 0.6 C.sub.2H.sub.4/C.sub.2H.sub.6 6 C.sub.2H.sub.6 4.42 0.1 1 GPU = 3.35 10.sup.10 mol m.sup.2 s.sup.1 Pa.sup.1

Example 2

[0151] In example 2, a PBZ-derived carbon membrane was manufactured according to the methodology described in example 1 with modifications to the curing protocol and the final pyrolysis temperature of the membrane. The PBZ-derived carbon membrane of example 2, designated as MCPBZ-5R/150-600, was prepared according to the following curing protocol: 80 C. for 30 min, 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min and 150 C. for 60 min. The final pyrolysis temperature was 600 C. To assess the performance of the developed membranes, pure gases He, CO.sub.2, O.sub.2, N.sub.2, CH.sub.4, C.sub.2H.sub.4 and C.sub.2H.sub.6 and results of the permeation tests are presented in Table 9.

TABLE-US-00009 TABLE 9 Gas permeabilities and selectivities of gas pairs obtained for a PBZ-derived carbon membrane (MCPBZ-5R/150-600) manufactured from the deposition of 5 layers of polymeric solution on a flat ceramic support and with final curing and pyrolysis temperatures equal to 150 C. and 600 C., respectively. MCPBZ-5R/150-600 Pure Kinetic Permeance gas diameter (GPU) Gas pairs Selectivity He 2.60 157 CO.sub.2/N.sub.2 38 CO.sub.2 3.30 75 CO.sub.2/CH.sub.4 375 O.sub.2 3.46 28 .sup.CO.sub.2/C.sub.2H.sub.4 25 N.sub.2 3.64 2 .sup.CO.sub.2/C.sub.2H.sub.6 375 CH.sub.4 3.80 0.2 O.sub.2/N.sub.2 14 C.sub.2H.sub.4 4.23 3 C.sub.2H.sub.4/C.sub.2H.sub.6 15 C.sub.2H.sub.6 4.42 0.2 1 GPU = 3.35 10.sup.10 mol m.sup.2 s.sup.1 Pa.sup.1

Comparative Examples 1 and 2

[0152] The PBZ-derived carbon membranes of comparative examples 1 and 2 showed similar gas transport properties, with the separation being characterized mainly by the molecular sieving mechanism. In these separation processes, gases with different kinetic diameters can be effectively separated, according to values obtained from selectivities to the evaluated industrial gas pairs. Furthermore, both membranes showed greater permeance through the membrane of ethylene gas molecules (C.sub.2H.sub.4) than methane gas molecules (CH.sub.4), which has a smaller kinetic diameter. This result can be related to the interaction of the remaining functional groups in the structure of the carbon membrane with ethylene gas molecules. Comparing examples 1 and 2, a greater permeation of pure gases is observed through the carbon membrane described in example 2, which may be related to the change in structure caused by the different final curing temperature (the CM in example 1 was crosslinked at 200 C., while the CM of example 2 was crosslinked at 150 C.) and by the possible reduction in thickness of the selective carbon layer with the increase in final pyrolysis temperature (final pyrolysis temperature equal to 500 and 600 C. for examples 1 and 2, respectively).

Example 3

[0153] In example, 3 PBZ-derived carbon membranes were manufactured according to the methodology described in example 1, but with 6 cycles of coating with polymeric solution on the flat ceramic support and with different curing protocols and a final pyrolysis temperature equal to 600 C. Membranes designated MCPBZ-6R/25-600, MCPBZ-6R/150-600, MCPBZ-6R/200-600, MCPBZ-6R/220-600 and MCPBZ-6R/250-600 were prepared.

[0154] The curing protocols used to manufacture the CM in this example are described below: [0155] MCPBZ-6R/25-60025 C. for 72 h. [0156] MCPBZ-6R/150-60080 C. for 30 min, 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min and 150 C. for 60 min. [0157] MCPBZ-6R/200-60080 C. for 30 min, 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 60 min, 180 C. for 60 min and 200 C. for 90 min. [0158] MCPBZ-6R/220-60080 C. for 30 min, 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min, 120 C. for 30 min, 130 C. for 30 min, 150 C. for 60 min 180 C. for 60 min and 200 C. for 90 min and 220 C. for 60 m. [0159] MCPBZ-6R/250-60080 C. for 30 ml 90 C. for 30 min, 100 C. for 30 min, 110 C. for 30 min 120 C. for 30 min 130 C. for 30 ml, 150 C. for 60 min, 180 C. for 60 min and 200 C. for 90 min, 220 C. for 60 min and 250 C. for 30 min.

[0160] To assess the performance of the developed membranes, pure gases CO.sub.2, O.sub.2, N.sub.2, C.sub.2H.sub.4 and C.sub.2H.sub.6 were used, and results of the permeation tests are presented in Tables 10 and 11.

TABLE-US-00010 TABLE 10 Permeabilities of pure gases through PBZ-derived carbon membranes manufactured from the deposition of 6 layers of polymeric solution on the flat ceramic support and different curing temperatures, as described in the table, and a final pyrolysis temperature of 600 C. Maximum curing temperature Permeability (Barrer) Membrane ( C.) CO.sub.2 O.sub.2 N.sub.2 C.sub.2H.sub.4 C.sub.2H.sub.6 MCPBZ-6R/25-600 25 504 220 24 15 2 MCPBZ-6R/150-600 150 488 187 12 19 0.8 MCPBZ-6R/200-600 200 350 154 19 10 0.4 MCPBZ-6R/220-600 220 390 163 13 15 2.4 MCPBZ-6R/250-600 250 98 33 5 9 0.8 Selective carbon layer thickness = 8 m 1 Barrier = 3.35 10.sup.16 mole m m.sup.2 s.sup.1 Pa.sup.1

TABLE-US-00011 TABLE 11 Selectivity to gas pairs obtained from carbon membranes derived from PBZ manufactured from the deposition of 6 layers of polymeric solution on the flat ceramic support and different curing temperatures, as described in the table, and a final pyrolysis temperature of 600 C. Maximum curing Optimal selectivity temperature CO.sub.2/ CO.sub.2/ CO.sub.2/ O.sub.2/ C.sub.2H.sub.4/ Membrane ( C.) N.sub.2 C.sub.2H.sub.4 C.sub.2H.sub.6 N.sub.2 C.sub.2H.sub.6 MCPBZ-6R/ 25 21 34 207 9 6 25-600 MCPBZ-6R/ 150 40 26 600 15 23 150-600 MCPBZ-6R/ 200 19 36 860 8 24 200-600 MCPBZ-6R/ 220 30 26 160 13 6 220-600 MCPBZ-6R/ 250 20 11 120 7 11 250-600

[0161] The PBZ-derived carbon membranes presented in example 3 showed that the main gas transport mechanism is molecular sieving and that there is an interaction between the chemical structure of the CM and the ethylene gas molecules. The curing protocol used in the development stage of the polymeric membrane influences the permeability of gases and the selectivity of the gas pairs assessed. Furthermore, it is observed that performance tests for PBZ-derived CM showed efficient selectivities for industrial gas separation processes.